Cellular communications systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive voice calls most anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate personal digital assistant (PDA) features such as calendars, address books, task lists, etc. Moreover, such multi-function devices may also allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example.
Even so, as the functionality of cellular communications devices continues to increase, so too does the demand for smaller devices which are easier and more convenient for users to carry. As a result, one style of cellular telephones which has gained wide popularity is the folding or “flip” phone. Flip phones typically have an upper housing with a display and speaker, and a lower housing or flap which carries the microphone. The keypad on such phones may be on either the upper housing or the lower housing, depending upon the particular model. The lower flap is connected to the upper housing by a hinge so that when not in use the upper and lower housings can be folded together to be more compact.
One example of a flip phone is disclosed in U.S. Pat. No. 5,337,061 to Pye et al. The phone has two antennas, a first one of which is mounted on the lower flap and includes a ground plane and an active monopole fed by a coaxial feed from electronic circuitry inside the phone. The flap is pivotally connected to the main or upper section of the housing, and is folded against the main section when not in use. Another similar antenna is fitted in the main section, and both antennas are connected to transceiver circuitry in the phone. The antennas are designed to introduce deliberate mismatch to provide an effective switching system between the antennas without the need for separate circuit elements.
The antenna configuration of a cellular telephone may also significantly effect the overall size or footprint of the phone. Cellular telephones typically have antenna structures that support communications in multiple operating frequency bands. Various types of antennas for mobile devices are used, such as helix, “inverted F”, folded dipole, and retractable antenna structures, for example. Helix and retractable antennas are typically deployed outside, i.e., on the exterior of, a mobile device, and inverted F and folded dipole antennas are typically within (i.e., on the interior of) a mobile device case or housing adjacent the top thereof.
Generally speaking, internal antennas allow cell phones to have a smaller footprint than do external antennas. Moreover, they are also preferred over external antennas for mechanical and ergonomic reasons. Internal antennas are also protected by the mobile device housing and therefore tend to be more durable than external antennas. External antennas may be cumbersome and make the mobile device difficult to use, particularly in limited-space environments.
Yet, one potential drawback of typical internal cellular phone antennas is that they are in relatively close proximity to the user's head when the phone is in use. As an antenna moves closer to a user's body, the amount of radio frequency (RF) energy radiation absorbed by the body will typically increase. The amount of RF energy absorbed by a body when using a mobile phone is called the specific absorption rate (SAR), and the allowable SAR for mobile phones is typically limited by applicable government regulations to ensure safe user RF energy exposure levels.
One attempt to reduce radiation exposure from cell phone antennas is set forth in U.S. Pat. No. 6,741,215 to Grant et al. This patent discloses various cellular phones with internal and external antenna configurations in which the antennas are positioned at the bottom of the phone to reduce radiation intensity experienced by a user, i.e., by moving the antenna farther away from the user's brain. Further, in some embodiments the housing of the phone forms an obtuse angle so that the bottom portion of the housing angles away from the user's face.
Despite such antenna configurations which allow for reduced radiation exposure, further advancements in antenna configurations, particularly internal antennas, may be desirable to allow for further reductions in overall device size while still providing relatively low SAR values.